Two University of Minnesota ethicists have set off a firestorm by raising questions about a controversial Texas stem-cell company.

In February, Leigh Turner, an associate professor at the University of Minnesota's Center for Bioethics, asked the Food and Drug Administration to investigate the company, Celltex Therapeutics, for selling stem-cell treatments that have not been proved safe or effective. That same month, his colleague Carl Elliott wrote an online article questioning the ethics of the company's own ethicist.

Within weeks, the online magazine Slate retracted Elliott's article under pressure from the company. Now, Celltex is demanding that the university denounce Turner's actions and remove his FDA letter from the Internet. In a March 9 letter to university President Eric Kaler, the company's lawyers said that Turner "alleged -- falsely -- that Celltex has engaged in various misconduct," and demanded to know if the letter "was authorized by the university."

The two professors call it a blatant attempt to silence criticism. "I contacted the FDA because I think it's a legitimate case for the FDA to investigate," said Turner, who says this is the first time he's filed such a complaint.

Turner says he's concerned that the company may be sidestepping federal rules, which are supposed to regulate and approve stem-cell treatments.

The company, however, says it does not administer stem cells "directly to patients," according to the letter to Kaler. It calls itself a lab that processes stem cells for physicians "who diagnose and prescribe to their patients."

Celltex and its lawyers did not respond to requests for comment on Monday.

But the story has lit up science blogs around the country.

"As Leigh Turner has carefully backed all his claims with hard evidence, I would certainly hope the University of Minnesota will stand by him," wrote one commenter Monday on Pharmalot.com.

The university released a brief statement later Monday, saying it was reviewing the matter but noting that faculty have "freedom to write on matters of public concern," as long as they make clear they're not speaking for the institution.

Turner, 43, said his clash with Celltex began about a month ago, when he sent some critical messages on Twitter about the company's newly hired medical ethicist, Glenn McGee.

Turner said he found it disturbing that McGee, who was editor of a prominent bioethics journal, would go to work for a company selling a treatment that had not gone through the FDA approval process. After the controversy went public, McGee resigned two weeks ago.

"This isn't just some mainstream pharmaceutical company," Turner said. Celltex, he said, reportedly charges $25,000 to $30,000 for banking and processing adult stem cells for treatments that have never gone through the FDA approval process. Elliott, Turner's colleague, wrote about the McGee case in a story published Feb. 17 in Slate. Two weeks later, Slate's editor withdrew the article with a published apology, saying the article "did not meet Slate's standards for verification and fairness." Elliott said the company had threatened to sue unless the article was removed. "I was very disappointed that they took it down," he said.

Meanwhile, on Feb. 21, Turner sent an eight-page letter to the FDA, urging an investigation into "whether their plan to administer stem cells to clients falls within the scope of federal law, peer-reviewed scientific research, evidence-based medicine, and ethical treatment of patients."

Last month, an investigation by the journal Nature also raised questions about Celltex's operations. It quoted a doctor who said Celltex paid him $500 to inject stem cells into patients, who pay $25,000 for the treatment. It also noted that one of Celltex's supporters is Texas Gov. Rick Perry, a former GOP presidential candidate, who received the adult-stem-cell treatment for back pain last year.